Join us as we mark the second global TK2d Awareness Day. Thymidine kinase 2 deficiency (TK2d) is a rare genetic mitochondrial disease that causes muscle issues often severely impacting a patient’s motor skills, breathing, and eating. TK2d is caused by inherited mutations in TK2, a nuclear gene responsible for making a mitochondrial enzyme called thymidine kinase 2. These mutations reduce the amount and quality of mitochondrial DNAs inside cells. Like all mitochondrial diseases, there is no FDA-approved treatment or cure.